4.9 ltr intermittent knock

[gresmi]

Good afternoon everyone!!

Last week I was driving my '91 DeVille back from the office and all seemed fine until I got home. My drive consists of mainly Interstate driving and it's about 18 miles. Everything seemed fine when I pulled into the driveway. I parked in the driveway and ran inside to change clothes, left the car running, and when I came back out I could hear a slight knock...or what sounded like a knock. I idled around the house for a few minutes and could hear the knock. I then drove it down the highway a few miles at 55 MPH then stopped again. When I stopped I couldn't hear the knock. I let the car sit a few hours, went back out, and started it again. After starting it I didn't hear the knock and drove it down the highway once again but still had no apparent knock.

Also, for a little more history. It's not unlikely for me to hear a knock when I first start the car up in the morning. It typically goes away as soon as I start to drive it or shortly after it warms up. I don't always hear it but it's for sure not uncommon. This is, I believe, the first time I have heard the knock after it has been driven for any length of time at highway or Interstate speeds. Of course, I'm thinking the worse, but figured I'd at least share my experience here in hopes someone else has had the same experience with their 4.9 ltr.

Since I have owned the car I have always thought that the amount of lubrication that you can see on the valves through the filler cap has seemed minimal. I'm use to looking through the valve covers and seeing oil on top of the head and coating valves. It seems when I look into this filler cap it seems dry. I know there is oil there but it's more like a 'film' of oil versus any excess. Again, it's always been this way and figured everything was Ok.

Thanks for reading my post.

Greg

[BodybyFisher]

The 4.9 has a #1 main bearing knock that can only be fixed if the #1 main bearing is replaced with an updated unit. It has to do with the serp belt pulling up on the crank at a specific angle that causes the knock. Highway speeds where the engine gets really hot or traffic will accent it

To remedy or minimize the situation, NEVER use a synthetic oil, my experience is that it magnifies the knock

Make sure the cooling system is up to par, and that the car runs cool, overheating the oil thins it out and you will hear the knock

If you want to totally minimize it use Rotella 15W40 diesel oil, your 4.9 will love it

By the way, one other thought, look at the oil to make sure there is no coolant leaking into it, it will look like chocolate milk, the cylinders are sealed via an oring that can leak coolant into the oil... The 4.9 is getting long on tooth and we have seen the orings fail

I had a 91 Seville 4.9

Let us know what you find out

[gresmi]

The 4.9 has a #1 main bearing knock that can only be fixed if the #1 main bearing is replaced with an updated unit. It has to do with the serp belt pulling up on the crank at a specific angle that causes the knock. Highway speeds where the engine gets really hot or traffic will accent it

To remedy or minimize the situation, NEVER use a synthetic oil, my experience is that it magnifies the knock

Make sure the cooling system is up to par, and that the car runs cool, overheating the oil thins it out and you will hear the knock

If you want to totally minimize it use Rotella 15W40 diesel oil, your 4.9 will love it

By the way, one other thought, look at the oil to make sure there is no coolant leaking into it, it will look like chocolate milk, the cylinders are sealed via an oring that can leak coolant into the oil... The 4.9 is getting long on tooth and we have seen the orings fail

I had a 91 Seville 4.9

Let us know what you find out

Thanks for the info BBF!!

I might give the Rotella a try. I run that in my truck and have gallons of it around. Currently I'm running Valvoline 10w-30 with a Mobile 1 filter. I have been using this combination now for the last 7-8 years.

I checked the oil yesterday and, other than being toward the bottom of the 'safe' mark the color appeared normal. Also, within the last 6 months, the old Caddy received a new radiator and fresh coolant. Although, since the day I installed the radiator it has a small leak some where in one of the lines but I haven't found it yet so it has used most of the coolant in the reservoir tank. I added coolant yesterday so we'll see how much it uses. I hope its simply leaking out and not leaking in.

Also, what I forgot to mention on my initial post, this knock came right after a WOT. I read on an old post last week about carbon buildup and to give the old car a few WOT, 2nd gear...WOT until 70-75 MPH. I did this without any issue and I only did it once. I didn't notice any smoke, white or black but it was shortly after that I heard the knock.

I love the car and it owes me nothing...I'd just like to keep around for another 100,000 miles or so!!

Thanks again for the response!!

Greg

[BodybyFisher]

Thanks for the info BBF!!

Also, what I forgot to mention on my initial post, this knock came right after a WOT. I read on an old post last week about carbon buildup and to give the old car a few WOT, 2nd gear...WOT until 70-75 MPH. I did this without any issue and I only did it once. I didn't notice any smoke, white or black but it was shortly after that I heard the knock.

I love the car and it owes me nothing...I'd just like to keep around for another 100,000 miles or so!!

Thanks again for the response!!

Greg

You are welcome Greg.

That WOT procedure you are talking about is for the 4.6 Northstar NOT the 4.9. The 4.9 does not develop the carbon knock.

Hopefully your engine will settle down and the WOT procedure did not do any damage. Taking the 4.9 to 75 in second gear raises the hair on the back of my neck....its not really recommended for it.

The 4.6 is a 32 valve, high compression high RPM revving engine that has a combustion chamber that will knock if carbon builds up, and the WOT procedure is recommended for that engine

Change the oil and go with 15W40 since you have it on hand, maybe you are hearing a valve lifter that collapsed a bit, I did that a couple of times winding out the engine...

Let us know how it turns out...

[gresmi]

Thanks for the info BBF!!

Also, what I forgot to mention on my initial post, this knock came right after a WOT. I read on an old post last week about carbon buildup and to give the old car a few WOT, 2nd gear...WOT until 70-75 MPH. I did this without any issue and I only did it once. I didn't notice any smoke, white or black but it was shortly after that I heard the knock.

I love the car and it owes me nothing...I'd just like to keep around for another 100,000 miles or so!!

Thanks again for the response!!

Greg

You are welcome Greg.

That WOT procedure you are talking about is for the 4.6 Northstar NOT the 4.9. The 4.9 does not develop the carbon knock.

Hopefully your engine will settle down and the WOT procedure did not do any damage. Taking the 4.9 to 75 in second gear raises the hair on the back of my neck....its not really recommended for it.

The 4.6 is a 32 valve, high compression high RPM revving engine that has a combustion chamber that will knock if carbon builds up, and the WOT procedure is recommended for that engine

Change the oil and go with 15W40 since you have it on hand, maybe you are hearing a valve lifter that collapsed a bit, I did that a couple of times winding out the engine...

Let us know how it turns out...

I'll give it a try. And, I didn't leave it in 2nd gear...it had shifted into 3rd gear before hitting 70 mph. I simply let the car shift into second...held WOT until 75 then let off. It was fun just not something I normally do.

And, so far so good. I definitely heard something after I did it but since then, I have driven the car twice and haven't heard anything else.

Also, would you recommend running the 15w-40 engine oil when it's cold out? I'm in Kansas, which is currently being covered in ice with our 2nd severe storm of the season. I think the high over the next few days will be in single digits (Fahrenheit).

Greg

[BodybyFisher]

You raise a good point, see this article from SHELL, you may find the 5W40 Rotella to make more sense. The thing with the diesel oil is the added zinc

http://www.shell.com...mn_Q8_2008.html

[gresmi]

You raise a good point, see this article from SHELL, you may find the 5W40 Rotella to make more sense. The thing with the diesel oil is the added zinc

http://www.shell.com...mn_Q8_2008.html

Thanks for the article...very interesting.

This might make for an entirely new post...what oil is everyone using. Also, I have always been worried about switching a high mileage motor from conventional to a synthetic oil. This too could be another post if others have done this without issue.

I think I'll do some research on the subject. If anyone else has any input please let me know. I usually keep the oil fresh in the car, never exceeding 3,000 miles...I always figured it was cheap insurance. I have an old truck on the farm with a worn 350 in it. It smokes and knocks all the time. A few years ago I switched to 10W-40 in the winter and 50w in the summer in hopes of prolonging the life. So far so good, she is still running. But, it does take some time for the oil to warm up. The oil pressure, when cold, is close to 80 psi so I baby it until it's warmed up.

Thanks for the help and quick responses!!

Greg

[BodybyFisher]

I think your 91 has an oil life monitor, changing your oil every 3000 miles is a waste of money and resources. If you have the OLM, reset and use it. There is a lot of science behind it, do a search here for 'oil life monitor' for the scientific background on it, Mike

Maybe use 5W in the cold months and 10W in the warmer months

[gresmi]

Yes, the car has a Oil Life Indicator on it. I know I change it well before the calculator says it's time but to me it's cheap insurance. I understand a lot of research has gone into the calculators but I think buying extra oil and extra filters is money well spent. I also try to use either Wix or Mobile filters whenever I can.

This is a hot topic in another forum I belong to for the LMM Duramax Diesel engine. The boys at GM have tried to think of everything to accurately determine the life of the oil and how to calculate motor load. The calculation also works with the transmission for throttle position versus gear selection versus speed to determine how hard the motor is working etc. It's a smart system, with the inputs it has it will vary both up shifts and downshifts. Some of the same data is also being used to calculate the life of the oil. It also logs pressures and ambient temperature. In the Diesel forum most still believe the calculator but you still find others that think it's all a gimmick. I do think it's probably accurate and a great tool to use...but with all the equipment I run on the farm and all the trucks I have running around, to drop the oil out of the old caddy or even a truck isn't a big deal. If it extends the life of even one motor it has paid for itself.

Anyway, sorry for getting a little side-tracked...wasn't my intent.

[BodybyFisher]

Cool, good luck and let us know how this turns out!, Mike

[the gold2]

This is an interesting thread , thanks Greg!

The WOT info is invaluable.

Regarding the 10W-40 oil use in a 4.9 liter engine, may I confirm with BodybyFisher that this weight of oil is fine to use instead of 10W-30 ?

My work horse car is a diesel and the Caddy is my fair-weather weekend car, so I have lots of 10W-40 stocked.

My hometown, San Francisco, has temperate climate where the winter may see very few 43F temps in morns or eves but the average is about 53F.

Summers are basic 65F to 72F.

Just want to make sure my 4.9 liter engine would be OK with 10W-40 oil since I have read on this forum otherwise.("the manufacturer says 10W-30, 'nuff said").

Thanks !

[gresmi]

This is an interesting thread , thanks Greg!

The WOT info is invaluable.

Regarding the 10W-40 oil use in a 4.9 liter engine, may I confirm with BodybyFisher that this weight of oil is fine to use instead of 10W-30 ?

My work horse car is a diesel and the Caddy is my fair-weather weekend car, so I have lots of 10W-40 stocked.

My hometown, San Francisco, has temperate climate where the winter may see very few 43F temps in morns or eves but the average is about 53F.

Summers are basic 65F to 72F.

Just want to make sure my 4.9 liter engine would be OK with 10W-40 oil since I have read on this forum otherwise.("the manufacturer says 10W-30, 'nuff said").

Thanks !

Gold2,

I think you are fine running the 10w-40 in your car. It's a heavier oil and won't be as efficient but I doubt you'll be able to tell the difference. I think any trade off for the heavier oil far out weighs any efficiency loss you will see in the motor. I will do the same thing to my car when it gets warmer outside. Last week it was -12 degrees here and there are times my old Caddy sits outside. Starting up any engine in temperatures like that is hard on them and the heavier oil not only takes longer to heat up and circulate it also adds pressure. Temperatures in your area, in my opinion, allows you to run the 10w-40 year around...where I'm at I'll run a lighter oil for 4-5 months.

Years ago a friend of mine, who is a mechanic and weekend racer, had a new 4.6 liter ford motor tore apart on his stand (for a customer). This was not long after Ford introduced the 4.6 liter motor. I was surprised to see the motor, which was so new, already being opened up. He blamed the trouble on two things, oil starvation and the weight of the oil. His claim/complaint was that Ford was using and recommending too light of an oil for the motor. He said that engine manufacturers were doing that to make the motors as efficient as possible. Now I'm not sure if any of that is true or not but it made sense to me and since then I haven't been afraid to run slightly heavier oil any many of my aging motors. In my opinion, the biggest risk you have is the oil pump and that you need to allow time for the oil to heat up before you put the motor under any significant load.

Greg

[the gold2]

Hey Greg, thanks for the reply. It makes sense. An afterthought I had was whether odometer mileage is a factor to consider for our 4.9 liter engines. Yours seems to have 100K and mine has 45K. Do you think mine would still OK with 10W-40 oil ?

Thanks.

[gresmi]

Hey Greg, thanks for the reply. It makes sense. An afterthought I had was whether odometer mileage is a factor to consider for our 4.9 liter engines. Yours seems to have 100K and mine has 45K. Do you think mine would still OK with 10W-40 oil ?

Thanks.

I don't think it hurts anything, just remember it's heavier oil and takes a little longer to warm up. It might add some additional strain to the oil pump but, if you don't try any WOT while it's cold, I don't think you'll have any issue(s).

I actually have two old Caddy's. The one I'm driving the most is the '91 DeVille and it has 142,000 miles on it. Great car and still the most comfortable vehicle I own. I also have a '90 that has 140,000 miles on it. I just bought it and haven't spent much time in it. It has a 4.5 liter motor that needs a little TLC.

From what I know the 4.9 liter motors were and still are reliable. Mine has a slight knock in it at startup, which it has had now for 30,000 to 50,000 miles (can't remember ever not hearing it...but not sure). It's amazing how many of these old C-cars you see still out on the road...which is a good sign. My '91 has never really given me much trouble. Every once in awhile I have to re-teach the 'high and low' idle, which takes about 15 minutes, but other than that it's been a great car.

It sounds like you have a good one or at least one that hasn't been used much. I know they like to be driven. When I bought my '91 it had just under 90,000 miles on it and it hadn't been driven much for 5-6 years prior. Once I bought it I immediately started to drive it, usually into the office which is 20 miles of highway driving one way. Had a few bugs to work out but since then it's been running well. Recently put a new radiator and catalytic converter in it. The converter was falling apart and sounded bad. Found that it was easier to just replace the converter rather than cut it out.

I hope you have good luck with your car too!! The people here are great and always seem to go out of their way to help if you ever have any trouble...so never hesitate to ask anything.

Greg

[the gold2]

Thanks Greg, I'll consider the other oil for the next oil change.

Yes indeed this forum is quite nice.

Many helpful and knowledgeable folks !

[BodybyFisher]

The nice thing about the diesel oils is their higher content of zinc, an anti-wear compound that is great for engines like the 4.9 and the early 4.6's (93 to 99). If i had a rubbing element lifter engine, I would use the Rotella or Delvac by Mobil diesel oils

[wdsj]

I use Rotella in my old cars (for the zinc - zddp) but have been told the zinc will destroy a cat converter.

Any opinions or experience?

[BodybyFisher]

I dont know how true that is because the guru who was on the Northstar Powertrain design team is who recommended us to use Rotella, so I am not concerned at all

[the gold2]

wdsj, I also have read in other sites' oil articles' caution about motor oil with zinc content in general due to 'apparent' reduction of cat converter life...

I suppose it depends on the amount of zinc and other things present. In fact basic motor oils just before and past the SJ rating had reduced zinc if any at all.(not referring to diesel rated)

You'd have to research the web for more details on motor oil.

I personally may consider half diesel rated and half regular gas rated 10W-40 to soften mental worries about the cat converter.

[trevor]

wdsj, I also have read in other sites' oil articles' caution about motor oil with zinc content in general due to 'apparent' reduction of cat converter life...

I suppose it depends on the amount of zinc and other things present. In fact basic motor oils just before and past the SJ rating had reduced zinc if any at all.(not referring to diesel rated)

You'd have to research the web for more details on motor oil.

I personally may consider half diesel rated and half regular gas rated 10W-40 to soften mental worries about the cat converter.

[trevor]

wdsj, I also have read in other sites' oil articles' caution about motor oil with zinc content in general due to 'apparent' reduction of cat converter life...

I suppose it depends on the amount of zinc and other things present. In fact basic motor oils just before and past the SJ rating had reduced zinc if any at all.(not referring to diesel rated)

You'd have to research the web for more details on motor oil.

I personally may consider half diesel rated and half regular gas rated 10W-40 to soften mental worries about the cat converter.

[trevor]

hi all,havent had the opportunity to be on the site for a while,as you know I have a 90 seville not sure how different this motor is to the 91 but the handbook says 10/40 oil is not recommended for this motor.Ihad big issues with this motor and knocking a few years ago ,ended up stripping the crankshaft out I was so certain it was cracked,There was no doubt I had been using too heavy engine oil after I shifted to a colder climate.Replaced the main bearings with 1/2 thou oversize which cadillac had in stock for the front and rear.Never had a knock again and have never run any more than 10/30 and I go back to 5/30 in winter.Just my thoughts on this subject,still love driving this car even if the 2000 gets most of the work.